Fluorine-based compounds are developed or used in wide applied fields of advanced materials, by virtue of characteristics of fluorine such as water repellency, oil repellency, low water absorption, heat resistance, weatherability, corrosion resistance, transparency, photosensitivity, low refractive index, and low dielectric property. In recent years in particular, resist materials employing fluorine-based compounds have actively been studied as novel materials that are highly transparent to short wavelength ultraviolet rays emitted by an F2 laser or ArF laser. A common molecular design in these applied fields is based on various performances such as photosensitivity using acid characteristics of fluoroalcohols having a 1,1,1,3,3,3-hexafluoroisopropyl-2-hydroxyl group (also referred to as a hexafluoroisopropyl hydroxyl group), adhesion to a substrate, and a high hardness, that is, a high glass transition point (Tg), in addition to transparency at each used wavelength due to the introduction of fluorine.
On the other hand, finer resist patterns have been more demanded with microfabrication of a device structure in lithography processes, so that improvements of exposure devices have been increasingly studied.
For example, a stepper (a reduction projection aligner) has been dramatically improved in resolution performance by performance improvements of reduction projector lenses and by refinements of optical designs. The performance of lenses used in the stepper is expressed by NA (numerical aperture), and its value of around 0.9 is defined as a physical limit in air but it has already been attained at the present time. With this, it is now on attempt to raise NA to 1.0 or more by filling a space defined between a lens and a wafer with a medium having a larger refractive index than air, in which an exposure technique that adopts an immersion method using pure water (hereinafter, which may be referred to as merely water) in particular as the medium has received attention (Non-Patent Publication 1).
In immersion lithography, various concerns resulted from contact between a resist film and the medium (e.g., water) have been pointed out. Particularly, there are problems such as changes in pattern shape and a pattern collapse due to swelling, which are caused by the water dissolving an acid generated in the film by exposure or an amine compound added as a quencher. In view of this, there is given a report that a topcoat layer disposed on the resist is effective at separating the resist film by water (Non-Patent Publication 2).
Hence a top coat composition is required to exhibit a good developing solution-solubility, resistance to pure water, separability between the resist film and water, and such a performance as not to affect the resist film disposed as underlayer. As a top coat composition satisfying the above-mentioned requirements, a composition that contains a fluorinated polymer formed of a repeating unit including a unit having two or more hexafluoroisopropyl hydroxyl group was developed, and the composition was reported to be excellent in developing solution-solubility in particular (Patent Publication 1).